As for a BIPOLAR-CMOS-DMOS (BCD) platform of 0.18 micrometers, after adding a mini-oxide structure of silicon dioxide material on a side of the channel region that is adjacent to the drain, the surface electric field of the LDMOS can be significantly reduced without increasing the region of the LDMOS, thereby addressing the degradation problem of the Idlin (linear drain current)/Rdson (on resistance) after a current and voltage test.
As to this mini-oxide, the conventional process utilizes silicon nitride as a hard mask to grow silicon dioxide via furnace tube and in certain region (i.e. the Local Oxidation of Silicon (LOCOS) technology). In particular, the silicon nitride can be used as a hard mask, a region that is required to have mini-oxide formed thereon is photo etched and defined, the silicon nitride in the region is etched away, the silicon dioxide grows in the furnace tube and on the device, and the silicon nitride is removed by phosphoric acid. However, the process has the following defect: as shown in FIG. 1, a large number of dislocations are introduced on the edge of the active region of the device, which will affect the reliability of the product.